A scan induction heat treatment process involves moving an elongated workpiece that generally has a length much larger than its cross sectional diameter through one or more scan inductors so that the workpiece can be heat treated, for example, in a quench hardening and/or tempering process. Either the entire length of the workpiece, or selected sections thereof, may be inductively heat treated. FIG. 1 is a simplified diagrammatic of a vertical scan induction process wherein the length of workpiece 90 passes through scan inductor 102. AC current is supplied to the scan inductor at terminals 102a and 102b from a suitable power source to establish the magnetic field that (flux) couples with the section of the workpiece moving through the inductor to inductively heat the workpiece. When the process includes quench hardening, the workpiece also passes through a quench dispersal apparatus, such as quench barrel 104, which has a series of quench holes 104a through which the quench medium (for example, water) passes to rapidly cool sections of the workpiece after they have been heated by passing through the scan inductor. In some arrangements the scan inductor and quench barrel may be incorporated into a single physical structure. The scan inductor and quench dispersal apparatus, if used, can be referred to as scan induction apparatus. A mechanical system is provided for holding the workpiece in position, and moving the workpiece through the scan inductor and quench barrel. The mechanical system may also rotate the workpiece as it moves through the scan inductor and quench barrel to achieve uniform heat treatment around the circumference of the workpiece. Therefore as diagrammatically illustrated in FIG. 1, the mechanical system typically includes an upper support element 112, with an upper center tooling element 112a attached to the upper support element, and a lower support element 116, with a lower center tooling element 116a attached to the lower support element. The lower center tooling is suitably attached to the workpiece so that rotational driver 114 can rotate the lower center tooling element and the attached workpiece as the workpiece moves linearly downward through the scan inductor. Upper support element 112 and upper center tooling element 112a are typically free spinning and capable of floating (sliding) in the vertical direction to account for workpiece longitudinal growth and shrinkage as the workpiece is heated and cooled. Further if the ends of the workpiece are heat treated, the upper and lower center tooling elements must be designed so as not to interfere with the heating of the ends. Linear driver 118 moves the upper and lower center tooling elements, with workpiece 90 positioned between these center tooling elements, in a vertical direction so that at least the length of the workpiece to be inductively heat treated passes through the scan inductor and quench barrel. For quench heat treatment, the linear drive will move the workpiece down through the scan inductor and quench ring with quench spray emitting from the quench holes while the workpiece is inductively heated. If tempering of the workpiece is desired after quench hardening, the linear drive can make a second pass of the workpiece through the scan inductor with no quench spray while the workpiece is inductively heated to a temperature required for tempering. In alternative designs, the workpiece may be fixed in position and the scan inductor and quench barrel may be moved over the length of the workpiece.
When the workpiece is particularly slender in cross sectional diameter relative to its length, there is a tendency for the workpiece to structurally deform, or warp, along its longitudinal axis between the time that a section of the workpiece is inductively heated by moving through the scan inductor, and quenched by moving through a quench spray emanating from the quench barrel. One example of such a workpiece is a socket wrench extension (bar) as shown in FIG. 2(b) that comprises a relatively slender and long metal rod, or shaft 90b, having a square fitting at a first end with a locking mechanism for locking a particular socket in place, and a female socket opening 90b at the opposing end for locking the extension bar in place on a socket wrench or another extension device. The female socket opening has an expanded cross section that is greater than the cross section of the shaft (including the square fitting at the first end of the extension bar). Deformation of a socket wrench extension during the induction heat treatment process renders the socket wrench extension unusable. Consequently subsequent to induction heat treatment, the socket wrench extension must be subjected to one or more industrial processes wherein the deformation is corrected to an acceptable tolerance.
It is one objective of the present invention to avoid such deformation of a workpiece during a scan induction heat treatment process.